“Resistance exercise is a potent stimulus for acute increases in the anabolic hormone concentrations such as growth hormone (GH) and testosterone (Kraemer et al., 1990; Goto et al., 2003). However, it is not clear whether acute increases in hormonal concentrations play a role in enhancements of muscular strength and muscle volume” (p. S303). The effects of magnitude of hormone responses to a single bout of resistance exercise session on muscular adaptations during prolonged training program were investigated. Males (N = 26) were assigned to either no-rest group, rest group, or control group. The training regimen in the no-rest group consisted of 5 sets of 10 repetition maximum (RM) with 1-minute rest periods between sets. In the regimen of rest group, Ss rested for 30 seconds immediately after five repetitions in each set. The no-rest and rest groups performed three exercises (lat pulldown, shoulder press, and bilateral knee extension) at the same number of lifts (with or without intraset rest) at the same relative intensity two days per week for 12 weeks. Acute hormonal responses to each regimen were initially assessed, and then muscular strength, endurance, and cross-sectional area were determined before and after training period.

In the no-rest group, concentrations of blood lactate, serum GH, plasma adrenaline and noradrenaline showed marked increases after acute exercise, whereas those in the rest group did not. Changes in muscular strength (1 RM, isometric and isokinetic strength) and endurance were significantly greater in the no-rest group than in the rest group. The cross-sectional area of the quadriceps femoris also showed a significantly greater increase in the no-rest group than in the rest group. A significant correlation was observed between peak value of post-exercise growth hormone concentration and change in cross-sectional area after 12 weeks of training. In the control group, no significant changes were observed in all variables.

Implication. These results suggest that the magnitude of acute growth hormone response may be important for anabolic adaptations during resistance training in young men. Effects of resistance training are compromised if rest periods are too long.